This invention relates to improvements in internal combustion engines operating on the Otto or four-stroke cycle, particularly to improvement of engine efficiency with minimum cost and change in present engine design and carburetion.
Various proposals have been made to improve the combustion efficiency of such engines, more recently directed toward reduction of unburned hydrocarbons and NO.sub.x in the exhaust emissions of the engine. Stratified charge and so-called "lean burn" engines are in various stages of development, and many of these trace their history to work done in the 1920's by Sir Harry Ricardo. A number of approaches have been reported, a typical summation appearing in Popular Science, July 1975, pages 56 et seq., and one engine in particular, the Honda CVCC engine is commercially available. It is a relatively small (75 cubic inch) four cylinder engine utilizing two separate intake valves and an inlet manifold and carburetor system which introduces a rich mixture in small amounts, then a leaner mixture.
While these proposals do in fact work, they are not easily adaptable to the much larger displacement engines used in the U.S. automotive industry. Cost is an important consideration in making any major engine design change, and future cost and acceptability is part of such consideration.
Prior art patents have suggested injection of air into the cylinder of such engines for various reasons. U.S. Pat. No. 2,011,986 discloses auxiliary air injection before and during combustion. It states that air injection should start near the middle of the compression stroke and end in the beginning of the firing stroke. U.S. Pat. No. 2,991,766 suggests injecting air into the cylinders during the expansion (power) stroke, and possibly continuing into the exhaust stroke. U.S. Pat. No. 2,994,310 suggests injecting air in the region near the spark plug during the period immediately following ignition. U.S. Pat. No. 3,019,777 also suggests air injection during the expansion stroke, entering around the spark plugs, and uses the ignition timing of related cylinders to control solenoid operated air valves to achieve the desired timing.
Another related approach is disclosed in U.S. Pat. No. 3,182,645, wherein air is injected just before ignition allowing the rich mixture around the spark plug to ignite before the injected air leaves the mixture. A dual land piston is used for air compression, together with special designs of piston top and cylinder head, requiring a completely reconstructed engine. U.S. Pat. No. 3,735,740 also teaches air injection around the spark plug just before firing, at the end of the compression stroke.
U.S. Pat. No. 3,792,691 discloses a spark ignition supercharged engine with twin exhaust valves, using injected Diesel fuel. It provides ports for additional air admission during the latter part of the intake stroke and beginning of the compression stroke, and again during the latter part of the power stroke and beginning of the exhaust stroke. This engine utilizes an exhaust gas turbo-supercharger and employs after-burning of gases in the exhaust manifold.
It will be noted that the various proposals set forth in the above mentioned earlier patents are somewhat contradictory, but it is believed that this may be due to different approaches to the complex problems of spark ignition Otto cycle engines, and to the many compromises in fuel-air mixing and supply which have been made in order to provide reliable high power automotive service, which inherently demands a wide range of engine speeds and power. With increasing emphasis on fuel economy and emmission control, these compromises are no longer desirable, but still there is a need for wide speed and power ranges, together with a need to adapt present engines so as to minimize tooling and improvement costs.